[wpilib] Add EventLoop (#4104)

This is a generic expansion of the command-based Trigger framework.

wpilibc/src/main/native/cpp/event/BooleanEvent.cpp

@@ -0,0 +1,64 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "frc/event/BooleanEvent.h"
+
+using namespace frc;
+
+BooleanEvent::BooleanEvent(EventLoop* loop, std::function<bool()> condition)
+    : m_loop(loop), m_condition(std::move(condition)) {}
+
+BooleanEvent::operator std::function<bool()>() {
+  return m_condition;
+}
+
+bool BooleanEvent::GetAsBoolean() const {
+  return m_condition();
+}
+
+void BooleanEvent::IfHigh(wpi::unique_function<void()> action) {
+  m_loop->Bind(m_condition, std::move(action));
+}
+
+BooleanEvent BooleanEvent::operator!() {
+  return BooleanEvent(this->m_loop, [lhs = m_condition] { return !lhs(); });
+}
+
+BooleanEvent BooleanEvent::operator&&(std::function<bool()> rhs) {
+  return BooleanEvent(this->m_loop,
+                      [lhs = m_condition, rhs] { return lhs() && rhs(); });
+}
+
+BooleanEvent BooleanEvent::operator||(std::function<bool()> rhs) {
+  return BooleanEvent(this->m_loop,
+                      [lhs = m_condition, rhs] { return lhs() || rhs(); });
+}
+
+BooleanEvent BooleanEvent::Rising() {
+  return BooleanEvent(
+      this->m_loop, [lhs = m_condition, m_previous = m_condition()]() mutable {
+        bool present = lhs();
+        bool past = m_previous;
+        m_previous = present;
+        return !past && present;
+      });
+}
+
+BooleanEvent BooleanEvent::Falling() {
+  return BooleanEvent(
+      this->m_loop, [lhs = m_condition, m_previous = m_condition()]() mutable {
+        bool present = lhs();
+        bool past = m_previous;
+        m_previous = present;
+        return past && !present;
+      });
+}
+
+BooleanEvent BooleanEvent::Debounce(units::second_t debounceTime,
+                                    frc::Debouncer::DebounceType type) {
+  return BooleanEvent(
+      this->m_loop,
+      [debouncer = frc::Debouncer(debounceTime, type),
+       lhs = m_condition]() mutable { return debouncer.Calculate(lhs()); });
+}

wpilibc/src/main/native/cpp/event/EventLoop.cpp

@@ -0,0 +1,30 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "frc/event/EventLoop.h"
+
+using namespace frc;
+
+EventLoop::EventLoop() {}
+
+void EventLoop::Binding::Poll() {
+  if (condition()) {
+    action();
+  }
+}
+
+void EventLoop::Bind(std::function<bool()> condition,
+                     wpi::unique_function<void()> action) {
+  m_bindings.emplace_back(Binding{condition, std::move(action)});
+}
+
+void EventLoop::Poll() {
+  for (Binding& binding : m_bindings) {
+    binding.Poll();
+  }
+}
+
+void EventLoop::Clear() {
+  m_bindings.clear();
+}